Police were called to Peterson's home on the 700 block of North 9th Avenue East on July 6th on reports of the baby girl not breathing.

According to the criminal complaint, Peterson put the child to sleep around 9 p.m. on July 5.

He admitted to authorities that on several occasions he had become frustrated with the child's crying, and to stop her he placed his hand over her mouth and pinched her nostrils closed until she stopped fussing.

He said he had done this approximately six times in the past, but that in each case he checked to make sure she was still breathing.

He said on July 5th, he put her to bed after covering her mouth and pinching her nostrils.

He said he did that until she stopped struggling.

He then lay the baby, face-down, in the crib and went downstairs to smoke marijuana.

He told police he didn't check on the child until the next morning.

Peterson said he didn't understand how the act would kill the baby because every other time she started breathing again.

He didn't say anything to the child's mother, who was home at the time, but unaware of the fact that he had suffocated the baby before putting her in her crib.

St Louis County Attorney Mark Rubin says Peterson is facing second degree unintentional murder charges because the attorney's office says he unintentionally took the life of the child while committing a felony assault on the infant.

However, St. Louis County says they are looking at the evidence to determine whether to call a grand jury to consider more serious charges.

"If evidence bears out, if reports support that there's a pattern of abuse of this child, or other people in the household, it could be grounds for murder in the first degree," says St Louis County Attorney, Mark Rubin.

"It's a very tragic situation. And extremely tragic for one family member to be responsible for the death of another so keep in mind and remember to keep in your thoughts the family of this victim and the small child," says Deputy Chief Ann Clancey, with the Duluth Police Dept.

Peterson is currently on probation for a misdemeanor domestic assault charge against the child's mother.

He has a criminal record involving escape from custody and several thefts of a motor vehicle charges and card fraud.

Peterson is looking at 40 years behind bars but it would be longer is he is charged with first degree murder.